linux-kernel - Re: attempt to scan fails (device busy) if essid/ssid was changed recently

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Message-Id: <1239109001.22453.40.camel@johannes.local>
Date:	Tue, 07 Apr 2009 14:56:41 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	linux-wireless <linux-wireless@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: attempt to scan fails (device busy) if essid/ssid was changed
 recently

On Tue, 2009-04-07 at 15:51 +0300, Maxim Levitsky wrote:

> > > I noticed that always first attempt at scan fails when NM asks for scan.
> > > I also noticed that this happens with quite recent kernels (I think
> > > 2,6.28) didn't have this behavior.
> > 
> > I'm pretty sure it did.

> I am sure that on older kernel there was no -EBUSY error returned to
> userspace. It probably just stalled the client.

Can't imagine it did, maybe it just dropped the request though without
indicating an error.

> > > Looking a bit deeper I discovered that each time NM disconnects from a
> > > networks it sets random ssid/essid to the card (using wireless
> > > extensions)
> > 
> > This forces a scan
> > 
> > > After that scan fails for some time.
> > > 
> > > as a NM free example you can run 
> > > 
> > > iwconfig wlan0 essid dummy
> > > iwlist scan
> > 
> > and then this fails with EBUSY.
> Thanks for explanation.
> Since NM has its reasons to clear essid (to prevent unwanted
> association), then what can be  done to prevent this (and still use
> wireless extensions, since nl80211 support isn't yet mature)?

Nothing. Wext sucks, news at 11, yadda.

johannes

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